The present invention relates to a power electronics module comprising a metal substrate, a printed circuit card carried on one of the faces of the substrate, and components, at least some of which are power components, mounted on the card which also carries electrical interconnection means between the components themselves and with an external power supply. A major, although non-exclusive, application of the invention lies in the field of automotive electronics in which certain systems incorporate components that carry high currents in operation, particularly active components such as switching transistors, and possibly also passive components such as capacitors or chokes.
The use of printed tracks on the card gives rise to considerable resistive losses because of the relatively small right cross-section of the tracks and thus of their high resistance. To limit such losses, the cards of some present-day modules are provided with a circuit constituted by bars fitted to the card. That structure, referred to as a bus bar structure, presents significant drawbacks. The design of the layout needs to be specific for each new type of module. Installation requires a high degree of planeness, which is difficult to achieve. The bars constitute a significant volume of copper.
An object of the present invention is to provide a power electronics module that satisfies practical requirements better than previously known modules, in particular in that the additional components used thereby are simple in structure and standardizable so that a new type of module does not require any complex design work.
To this end, the invention provides in particular a module wherein the interconnection means include conductive bridges of a shape enabling them to extend over a power component and mutually interconnecting short segments of interconnection tracks that carry power currents.
The bridges are advantageously staple-shaped, most or all of them having the same dimensions of length and height that are sufficient to enable each of them to straddle a power component, or at least each of the active power components that are usually identical or comparable in size. Thus most or all of the bridges can be identical and of size little greater than that of the component, thereby enabling them to be handled as thought they were components, and in particular enabling them to be put into place by automatic machines after the components have been assembled.
The ends of the bridges are generally soldered to the segments using the same method as is used to solder the components, for example reflow soldering of areas of lead-tin solder when the bridges are made of copper and possibly pre-tinned.
To reduce resistive losses and heating, the short segments can be given a cross-section that is greater than that of controlling equipotential tracks that are also printed on the card. The length of the segment will always be considerably shorter than that of the bridges.
The printed circuit can be single layer or multilayer. One of its faces, an insulating face, is bonded to the substrate. In general, the substrate is carried by a cooled wall or contains a circuit for a cooling fluid, particularly if the module is to be placed in a high-temperature environment in operation, for example in the engine compartment of a motor vehicle.
The invention also provides a method of manufacturing a module, in which:
a printed circuit card carrying equipotential tracks and segments of conductor track of section greater than that of the equipotential tracks is fixed on one face of a metal substrate;
solder or brazing areas are placed at locations of the tracks for being connected to components or to bridges of conductive metal;
the components are placed in such a manner as to enable them to be secured by soldering;
the bridges are placed at locations such that their ends bear against solder or brazing areas and the bridges interconnect said segments to one another; and
the components and the bridges are fixed definitively, generally by reflow soldering.
The above characteristics and others will appear better on reading the following description of a particular embodiment given by way of non-limiting example. The description refers to the accompanying drawing.